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Disperse Systems part 1 Flashcards Preview

What is a dispersed system?

Un-dissolved globules (liquid) or particels (solid) mixed throughout another phase

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What do disperse systems consist of?

2 or more components in a heterogenous mixture

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What is a heterogenous mixture?

A non-uniform mixture of smaller constituent parts

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What are the phases in a dispersed system and what do they mean?

DISPERSED PHASE: small droplets/particles that are seperated and dispersed throughoutCONTINUOUS PHASE or DISERSANT is the remainder of the formulation in which the small droplets or particles are dispersed in.

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What can the continuous or disperse phases be?

Solid, liquid or gas

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What type of disperse system is solid particles dispersed in a liquid continuous phase?

A solution

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What type of disperse system is liquid globules in a liquid continuous phase?

An Emulsion

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What is a liquid or solid phase dispersed in gas?

A liquid or solid AEROSOL.

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How do we want the dispersed particles to be?

We want the dispersed particles to be of the same size, and be very small to reduce the effect of gravity (take longer for the dispersed particles to fall to the bottom.)

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What is the name on dispersed particles of different size, and what happens to the particles?

Poly-dispersed - not likely to be seen in pharmacy. The small particles get squished by the large particles causing them to stick together.

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What happens if the particles in the dispersed phase are very large?

The gravity will have a greater effect, and cause the particles to fall to bottom (sedimentation)

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There are two different sizes of dispersions:

Colloidal and coarse

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What is the size of colloidal dispersions?

Tiny particle size about 1nm to 1µm

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What is the size of coarse dispersions?

Bigger particle size of more than 1µm

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Properties of an ideal disperse system (list 5)

1) Uniform particle size (not poly-dispersed)2) Small particle size3)Particles must not sediment too rapidly (will do eventually)4) Any sediment must be easily re-dispersed5) Must easily flow out of the container (will need a balance between being too thick to flow out and too thin that sediments too quickly)

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How do we want the surface are of the drug to be in a dispersed system? What does nature want?

We want to break the drug up for larger surface area to reduce sedementation, but nature doesn't like lots of energy in the system so will try to reduce the surface area by clumping the particles together to decrease the surface area.

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What are the advantages of a dispersed system?(4)

1) Drugs that are susceptible to aqueous degredation (break down when in contact with water) may be formulated as a suspension2) Improved bioavailibility compared to a solid due to the smaller particle size and therefore increased surface area for metabolism.3) Particle size can control absorption rates so if extended absorption was required, then could create a poly-dispersed system where the small molecules would be absorbed quickly and the larger molecules slower.4) Allows flexibility of formulation e.g. masking bitter taste.

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Why is it possible to formulate a suspension with drugs susceptible to aqueous degredation?

The drug is put into the water as solid particles and therefore the chemistry of the molecule is less likely to be damaged by hydrolysis. The outside of the 'clump' of particles may be effected, but the inside won't.

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Why can't drugs susceptible to aqueous degredation be in a solution?

Because the particles would be evenly distributed and the chemistry of the molecules will be damaged by hydrolysis.

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What are the diadvantages of Disperse systems?(2)

1) If not shaken or re-dispersed when shaken, accurate dosing cannot be assured.2) It is a liquid medicine so there is water present so must be careful of contamination.

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Optical Properties of disperse systems:

They are too small to be visible to the human eye, but are large enough to interfere with the path of light travelling through.

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What will happen when light passes through a suspension?

The light will pass through if it doesn't come to contact with any particles, but will be scattered if it comes to contact with particles.

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What will effect the degree of light scattering?

The size of the particles:Small particles = scater ("bend") the light moreLarge particles = Scater the light less

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What property can be used to determine thr Molecular weight , and give information on particle size and shape?

The degree of light scattering, and the fact that small particles will "bend" the light more than large particles.

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What is turbidity?

The cloudiness of the fluid

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What causes a dispersion to appear turbid?

Light scattering causes the dispersion to be turbid

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How can turbidity be used to measure concentration?

the more concentrated the dispersion, the more light is scattered and the more turbid the dispersion looks.

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What is Laser Diffraction?

Similar to light, but laser only has ONE WAVELENGTH. If nothing is in the way of a laser beam then the laser will pass through and hit the detector in the middle. If the laser beam will come to contact with a particle, the beam will be sacttered, and won't hit the middle of the detector.

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What does the amount of bending from a laser beam predict about the particles?

It predicts the size of the paricles - the further from the middle of the detector the beam is, the smaller the particle size (the smaller the particle size, the more bending of the laser beam).

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What does the laser beam tell about poly-dispersement?

Because the laser beam is a single wavelength, if it hits the detector at different sites, then we know that the particle sizes are different so poly-dispersed.

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What will affect laser beam scattering other than particle size?

The wavelength (colour) of the light - Blue light has a short wavelength and is scattered more than red light which has a long wavelength.